This instrument, which may have been made by James Kynvyn in 1595, is now incomplete. Only half of the horizontal circle, with the degree scale, remains (from 180 to 360?). This contains the support for the compass, which is now missing. A quadrant with its nonius is raised orthogonally on this base. An alidade, which is now missing, was pivoted at the right angle of the second plate. This allowed heights to be measured, while the compass gave readings of the angles of position.

The instrument allowed the co-ordinates of celestial bodies to be calculated (height above the horizon and position with respect to the magnetic meridian).